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Basics of Telephony
Overview Thou Art Welcome To The Dungeons Of Telephony! The Dark Labirynths Of Twisted Pairs And Local Exchange Castles Thou Shall Pass To Proceed To The Next Level! Beware of Angry Trolls! Godspeed! Phone A telephone remains one of the simplest devices ever 9/28/10 Slide 25 Making A Phone Call Step 1: 'Picking up the handset completes the '''circuit '''between the phone and the '''local exchange office'http://communication.howstuffworks.com/telephone.htm '''Step 2: '''Call leaves through the '''pair of copper wires connected from your house to the "entrance bridge"http://communication.howstuffworks.com/telephone.htm Step 3: Entrance bridge then proceeds the call to the digital concentrator, whicn digitizes the the signal at a sample rate of 8,000 samples per second and 8-bit resolution. Step 4: 'Concentrator sends the digitized signal to the '''local exchange, '''which then routes the call to the '''main exchange.'http://communication.howstuffworks.com/telephone.htm (NOTE: If the phone you are calling is connected to the same local exchange switch then it just creates the loop between your phone and the phone you are calling skipping the main exchange.) '''Step 5: '''Main exchange then may reroute the call to another main exchage or to an international exchange depending on where the call is going. International calls are sent through the satellites or undersea cables.http://communication.howstuffworks.com/telephone.htm Visualization Long Distance Call Long distance calls travel through the following route: '''Local Office Switch'' (access database,'' look up PIC) -> Long Distance Switch -> Local Carrier. PIC Code - Primary Interchange Carrier Code, indicates the long distance carrier 9/28/10 Slide 29 Public Switched Telephone Network PSTN, '''also refered to as POTS (Plain Old Telephone System), is the network of the world's public circuit-switched telephone networks. http://en.wikipedia.org/wiki/Public_switched_telephone_network 'Functions of a network ' 9/28/10 Slide 31 *access *transport *switching *service delivery '''Components of a PSTN 9/28/10 Slide 31 *signaling *access and switching *transport *customer-premises equipment (CPE) Regional Bell Operating Companies RBOC's are the local exchange service operating companies originally derived from AT&T Corp. in 1984. Originally there were 7 "Baby Bells", but many of the merged leaving only 3 RBOC's today: AT&T, Verizon, and Qwest. http://en.wikipedia.org/wiki/Regional_Bell_Operating_Company#Mergers Local Access & Transport Area (LATA) - area within which RBOC is permitted to offer exchange telecom and access services. 9/28/10 Slide 33 Exchange Carriers Local Echange Carrier (LEC) - local telephone company 9/28/10 Slide 34 *Incumbent LEC - existed before RBOC's split *Competitive LEC- competes with other already estblished companies Interexchange Carrier (IXS or IEC) - long distance telephone company 9/28/10 Slide 34 *Point Of Presence (POP) - area where IXC could terminate services and provide connections into LATA Local Loop - Line from local telephone company to the end user's premis (access line) 9/28/10 Slide 33 Carrier Identification Code (CIC) '- a code used for billing and call routing 9/28/10 Slide 47 Signaling 'Four basic function of signaling '''9/28/10 Slide 37 #Alerting #Transmitting information signals #Transmitting address info #Supervising circuit status, network management '''Alerting (someone's calling): Ringer - 20 Hz sine wave, 2 seconds on, 4 seconds off 9/28/10 Slide 40 Info Signals: Dial tone, Ring Back tone, Line Busy tone, Trunk Busy tone 9/28/10 Slide 41 Addressing: Dual Tone Multy Frequency (DTM'F) - each number on the keypad is a combination of two different frequencies. 9/28/10 Slide 42 '''Numbering Plan: '''9/28/10 Slide 43 *International Dialing Code - Country Code *Area code (first digit restricted to 2-9) - 3 digits *Exchange Code (first digit restricted to 2-9) - 3 digits *Subscriver Code - 4 digits Ex: 1 517 580 5555 'Modern Signaling Systems: SS7 ''' http://en.wikipedia.org/wiki/Signaling_System_No_7#Signaling_modes '''Signaling System #7 (SS7) is a set of telephony signaling protocols which are used to set up most of the world's public switched telephone network telephone calls. 'In-band signaling vs. Out-of-band signalin'g 9/28/10 Slide 48 In-band - voice and signaling are transferred through the same channel (Ex: DTMF) Out-of-band - voice and signaling data travel on separate trunks (Ex: SS7) Switching *Public vs. Private *Manual vs. Electronic *Analog vs. Digital *Circuit Switched vs. Packet Switched 9/28/10 Slide 50 Transport Carriage of conversations over trunks multiplexed 9/28/10 Slide 52 *digital *T1 - most common trunk T1 combines 24 separate voice channels onto a single link. The T1 data stream is broken into frames consisting of a single framing bit plus 24 channels of 8-bit bytes.9/28/10 Slide 53 Business phone systems PBX Private Branch Exchange - telephone exchange that serves a particular business or office; moves a portion of a Central Office to a customer premise 9/28/10 Slide 56 KTS Allowed the station user to see and control the calls directly (lighted line buttons) CENTREX *PBX-like *CO operated *PROS: Investment and operating cost, Networking *CONS:Limited features, Lack of control 9/28/10 Slide 58-59 The Grand Finale thumb|326px|left [[Wireless Telephony|'CONTINUE... ']] [[TC201 Giga Wiki|'MENU ']] References